1. Field of the Invention
The present invention relates to a method for detecting an occupation of an adjacent channel by a signal with the aid of a complex-valued bandpass signal having an information channel component and/or an adjacent channel component. The invention further relates to a corresponding device for detecting an occupation as well as a transmitting/receiving device and an integrated circuit having such a device.
2. Description of the Background Art
The invention is in the field of telecommunications. In particular, it is in the field of telecommunications systems, in which a number of transmitting/receiving devices access spectrally separated (carrier frequency) channels according to the frequency-division multiple access (FDMA) method. In this context, it is necessary in the receiving unit of each transmitting/receiving device to ensure, firstly, that the data received through its “own” channel (“information channel”) is correctly detected, even when data of other transmitting/receiving devices is simultaneously being transmitted in a spectrally adjacent channel (“adjacent channel”), and the received signal therefore contains information channel components and adjacent channel components. It is also necessary to ensure that data transmitted in an adjacent channel and not intended for this transmitting/receiving device is not detected even if no data is being transmitted in the information channel and the received signal therefore contains only an adjacent channel component.
Adjacent channel signal components are typically suppressed in the receiving units of the transmitting/receiving devices by analog receive filters having adequately steep filter slopes. One disadvantage of this is that such receive filters are complex in their design and are thus cost-intensive. The complex design is also accompanied by an increased power consumption of the receive filter. Implementation expenses and power consumption increase further when measures must be taken to compensate for the variations in value of the components used for the analog receive filter resulting from production tolerances, temperature effects and/or aging effects.
Although they are applicable to any desired FDMA telecommunications systems, the present invention and the problem on which it is based are described below using a “ZigBee” communications system per IEEE 802.15.4.
So-called “Wireless Personal Area Networks” (WPANs) may be used for wireless transmission of information over relatively short distances (approximately 10 m). In contrast to Wireless Local Area Networks (WLANs), WPANs require little, or even no, infrastructure for data transmission, so that small, simple, energy-efficient and low-cost devices can be implemented for a wide range of applications.
IEEE Standard 802.15.4 specifies low-rate WPANs which, with raw data rates of up to 250 kbit/s and fixed-position or mobile devices, are suitable for applications in industrial monitoring and control, in sensor networks, in automation, as well as in the field of computer peripherals and for interactive games. The ability to implement the devices very simply and economically is critical for such applications, as is an extremely low power requirement. Hence, this standard aims for battery lifetimes of several months to several years.
At the level of the physical layer, IEEE Standard 802.15.4 specifies a total of 16 (carrier frequency) channels at 5 MHz intervals in the ISM band (industrial, scientific, medical) around 2.4 GHz, which is available almost worldwide. For raw data rates of 250 kbit/s a symbol-value-specific PN band spread (pseudo noise spreading) with a chip rate of fC=2 Mchip/s and offset QPSK modulation (quaternary phase shift keying) is provided in these channels.
Data transmission is chiefly accomplished with the use of frames. The actual useful data (data payload, MSDU) here are augmented on the transmit side at the level of the MAC layer (medium access control) by check and control data, such as a sequence number, address fields, and a frame check sequence. The resulting MAC frame (MPDU) is extended at the level of the physical layer by prepending additional control data, such as a synchronization header, which enables the receiving unit to synchronize and lock onto the data stream, to produce the data frame (PPDU) that is ultimately to be transmitted.
If the analog receive filters are designed with less steep slopes for reasons of complexity and energy consumption, and consequently the adjacent channel signal components are less strongly suppressed, the problem can arise that in situations where an adjacent channel signal is received but no information channel signal component is received, the adjacent channel data contained in the receive signal may be correctly detected as a result of the very high sensitivity of present-day receiving units and may be erroneously forwarded to the control unit of the transmitting/receiving device as information channel data. Not until the level of the MAC layer is it then determined in the control unit, for example by comparing the expected number or address with the actual number or address of the MAC frame (MPDU), that this frame is not intended for this transmitting/receiving device at all, for example, and must therefore be discarded. The complete data frame (PPDU) must be detected by the receiving unit before such a comparison of the numbers or addresses of the MAC frame (MPDU) can take place. A disadvantage here is that the receiving unit is unavailable during this period of time (duration of a PPDU) for detecting actual information channel data. A further disadvantage is that the control unit, which is often designed as a separate integrated circuit, consumes additional energy for the comparison of the numbers or addresses.